#!/bin/sh
#
# Copyright 2007 Andy Parkins
#
# This file is Copyright 2007 by the GPSD project
# SPDX-License-Identifier: BSD-2-clause
#
# An example hook script to mail out commit update information.  This hook
# sends emails listing new revisions to the repository introduced by the
# change being reported.  The rule is that (for branch updates) each commit
# will appear on one email and one email only.
#
# This hook is stored in the contrib/hooks directory.  Your distribution
# will have put this somewhere standard.  You should make this script
# executable then link to it in the repository you would like to use it in.
# For example, on debian the hook is stored in
# /usr/share/doc/git-core/contrib/hooks/post-receive-email:
#
#  chmod a+x post-receive-email
#  cd /path/to/your/repository.git
#  ln -sf /usr/share/doc/git-core/contrib/hooks/post-receive-email hooks/post-receive
#
# This hook script assumes it is enabled on the central repository of a
# project, with all users pushing only to it and not between each other.  It
# will still work if you don't operate in that style, but it would become
# possible for the email to be from someone other than the person doing the
# push.
#
# Config
# ------
# hooks.mailinglist
#   This is the list that all pushes will go to; leave it blank to not send
#   emails for every ref update.
# hooks.announcelist
#   This is the list that all pushes of annotated tags will go to.  Leave it
#   blank to default to the mailinglist field.  The announce emails lists
#   the short log summary of the changes since the last annotated tag.
# hooks.envelopesender
#   If set then the -f option is passed to sendmail to allow the envelope
#   sender address to be set
# hooks.emailprefix
#   All emails have their subjects prefixed with this prefix, or "[SCM]"
#   if emailprefix is unset, to aid filtering
# hooks.showrev
#   The shell command used to format each revision in the email, with
#   "%s" replaced with the commit id.  Defaults to "git rev-list -1
#   --pretty %s", displaying the commit id, author, date and log
#   message.  To list full patches separated by a blank line, you
#   could set this to "git show -C %s; echo".
#
# Notes
# -----
# All emails include the headers "X-Git-Refname", "X-Git-Oldrev",
# "X-Git-Newrev", and "X-Git-Reftype" to enable fine tuned filtering and
# give information for debugging.
#

# ---------------------------- Functions

#
# Top level email generation function.  This decides what type of update
# this is and calls the appropriate body-generation routine after outputting
# the common header
#
# Note this function doesn't actually generate any email output, that is
# taken care of by the functions it calls:
#  - generate_email_header
#  - generate_create_XXXX_email
#  - generate_update_XXXX_email
#  - generate_delete_XXXX_email
#  - generate_email_footer
#
generate_email()
{
        # --- Arguments
        oldrev=$(git rev-parse $1)
        newrev=$(git rev-parse $2)
        refname="$3"

        # --- Interpret
        # 0000->1234 (create)
        # 1234->2345 (update)
        # 2345->0000 (delete)
        if expr "$oldrev" : '0*$' >/dev/null
        then
                change_type="create"
        else
                if expr "$newrev" : '0*$' >/dev/null
                then
                        change_type="delete"
                else
                        change_type="update"
                fi
        fi

        # --- Get the revision types
        newrev_type=$(git cat-file -t $newrev 2> /dev/null)
        oldrev_type=$(git cat-file -t "$oldrev" 2> /dev/null)
        case "$change_type" in
        create|update)
                rev="$newrev"
                rev_type="$newrev_type"
                ;;
        delete)
                rev="$oldrev"
                rev_type="$oldrev_type"
                ;;
        esac

        # The revision type tells us what type the commit is, combined with
        # the location of the ref we can decide between
        #  - working branch
        #  - tracking branch
        #  - unannoted tag
        #  - annotated tag
        case "$refname","$rev_type" in
                refs/tags/*,commit)
                        # un-annotated tag
                        refname_type="tag"
                        short_refname=${refname##refs/tags/}
                        ;;
                refs/tags/*,tag)
                        # annotated tag
                        refname_type="annotated tag"
                        short_refname=${refname##refs/tags/}
                        # change recipients
                        if [ -n "$announcerecipients" ]; then
                                recipients="$announcerecipients"
                        fi
                        ;;
                refs/heads/*,commit)
                        # branch
                        refname_type="branch"
                        short_refname=${refname##refs/heads/}
                        ;;
                refs/remotes/*,commit)
                        # tracking branch
                        refname_type="tracking branch"
                        short_refname=${refname##refs/remotes/}
                        echo >&2 "*** Push-update of tracking branch, $refname"
                        echo >&2 "***  - no email generated."
                        exit 0
                        ;;
                *)
                        # Anything else (is there anything else?)
                        echo >&2 "*** Unknown type of update to $refname ($rev_type)"
                        echo >&2 "***  - no email generated"
                        exit 1
                        ;;
        esac

        # Check if we've got anyone to send to
        if [ -z "$recipients" ]; then
                case "$refname_type" in
                        "annotated tag")
                                config_name="hooks.announcelist"
                                ;;
                        *)
                                config_name="hooks.mailinglist"
                                ;;
                esac
                echo >&2 "*** $config_name is not set so no email will be sent"
                echo >&2 "*** for $refname update $oldrev->$newrev"
                exit 0
        fi

        # Email parameters
        # The email subject will contain the best description of the ref
        # that we can build from the parameters
        describe=$(git describe $rev 2>/dev/null)
        if [ -z "$describe" ]; then
                describe=$rev
        fi

        generate_email_header

        # Call the correct body generation function
        fn_name=general
        case "$refname_type" in
        "tracking branch"|branch)
                fn_name=branch
                ;;
        "annotated tag")
                fn_name=atag
                ;;
        esac
        generate_${change_type}_${fn_name}_email

        generate_email_footer
}

generate_email_header()
{
        # --- Email (all stdout will be the email)
        # Generate header
        cat <<-EOF
        To: $recipients
        Subject: ${emailprefix}$projectdesc $refname_type, $short_refname, ${change_type}d. $describe
        X-Git-Refname: $refname
        X-Git-Reftype: $refname_type
        X-Git-Oldrev: $oldrev
        X-Git-Newrev: $newrev

        This is an automated email from the git hooks/post-receive script. It was
        generated because a ref change was pushed to the repository containing
        the project "$projectdesc".

        The $refname_type, $short_refname has been ${change_type}d
        EOF
}

generate_email_footer()
{
        SPACE=" "
        cat <<-EOF


        hooks/post-receive
        --${SPACE}
        $projectdesc
        EOF
}

# --------------- Branches

#
# Called for the creation of a branch
#
generate_create_branch_email()
{
        # This is a new branch and so oldrev is not valid
        echo "        at  $newrev ($newrev_type)"
        echo ""

        echo $LOGBEGIN
        show_new_revisions
        echo $LOGEND
}

#
# Called for the change of a pre-existing branch
#
generate_update_branch_email()
{
        # Consider this:
        #   1 --- 2 --- O --- X --- 3 --- 4 --- N
        #
        # O is $oldrev for $refname
        # N is $newrev for $refname
        # X is a revision pointed to by some other ref, for which we may
        #   assume that an email has already been generated.
        # In this case we want to issue an email containing only revisions
        # 3, 4, and N.  Given (almost) by
        #
        #  git rev-list N ^O --not --all
        #
        # The reason for the "almost", is that the "--not --all" will take
        # precedence over the "N", and effectively will translate to
        #
        #  git rev-list N ^O ^X ^N
        #
        # So, we need to build up the list more carefully.  git rev-parse
        # will generate a list of revs that may be fed into git rev-list.
        # We can get it to make the "--not --all" part and then filter out
        # the "^N" with:
        #
        #  git rev-parse --not --all | grep -v N
        #
        # Then, using the --stdin switch to git rev-list we have effectively
        # manufactured
        #
        #  git rev-list N ^O ^X
        #
        # This leaves a problem when someone else updates the repository
        # while this script is running.  Their new value of the ref we're
        # working on would be included in the "--not --all" output; and as
        # our $newrev would be an ancestor of that commit, it would exclude
        # all of our commits.  What we really want is to exclude the current
        # value of $refname from the --not list, rather than N itself.  So:
        #
        #  git rev-parse --not --all | grep -v $(git rev-parse $refname)
        #
        # Gets us to something pretty safe (apart from the small time
        # between refname being read, and git rev-parse running - for that,
        # I give up)
        #
        #
        # Next problem, consider this:
        #   * --- B --- * --- O ($oldrev)
        #          \
        #           * --- X --- * --- N ($newrev)
        #
        # That is to say, there is no guarantee that oldrev is a strict
        # subset of newrev (it would have required a --force, but that's
        # allowed).  So, we can't simply say rev-list $oldrev..$newrev.
        # Instead we find the common base of the two revs and list from
        # there.
        #
        # As above, we need to take into account the presence of X; if
        # another branch is already in the repository and points at some of
        # the revisions that we are about to output - we don't want them.
        # The solution is as before: git rev-parse output filtered.
        #
        # Finally, tags: 1 --- 2 --- O --- T --- 3 --- 4 --- N
        #
        # Tags pushed into the repository generate nice shortlog emails that
        # summarise the commits between them and the previous tag.  However,
        # those emails don't include the full commit messages that we output
        # for a branch update.  Therefore we still want to output revisions
        # that have been output on a tag email.
        #
        # Luckily, git rev-parse includes just the tool.  Instead of using
        # "--all" we use "--branches"; this has the added benefit that
        # "remotes/" will be ignored as well.

        # List all of the revisions that were removed by this update, in a
        # fast forward update, this list will be empty, because rev-list O
        # ^N is empty.  For a non fast forward, O ^N is the list of removed
        # revisions
        fast_forward=""
        rev=""
        for rev in $(git rev-list $newrev..$oldrev)
        do
                revtype=$(git cat-file -t "$rev")
                echo "  discards  $rev ($revtype)"
        done
        if [ -z "$rev" ]; then
                fast_forward=1
        fi

        # List all the revisions from baserev to newrev in a kind of
        # "table-of-contents"; note this list can include revisions that
        # have already had notification emails and is present to show the
        # full detail of the change from rolling back the old revision to
        # the base revision and then forward to the new revision
        for rev in $(git rev-list $oldrev..$newrev)
        do
                revtype=$(git cat-file -t "$rev")
                echo "       via  $rev ($revtype)"
        done

        if [ "$fast_forward" ]; then
                echo "      from  $oldrev ($oldrev_type)"
        else
                #  1. Existing revisions were removed.  In this case newrev
                #     is a subset of oldrev - this is the reverse of a
                #     fast-forward, a rewind
                #  2. New revisions were added on top of an old revision,
                #     this is a rewind and addition.

                # (1) certainly happened, (2) possibly.  When (2) hasn't
                # happened, we set a flag to indicate that no log printout
                # is required.

                echo ""

                # Find the common ancestor of the old and new revisions and
                # compare it with newrev
                baserev=$(git merge-base $oldrev $newrev)
                rewind_only=""
                if [ "$baserev" = "$newrev" ]; then
                        echo "This update discarded existing revisions and left the branch pointing at"
                        echo "a previous point in the repository history."
                        echo ""
                        echo " * -- * -- N ($newrev)"
                        echo "            \\"
                        echo "             O -- O -- O ($oldrev)"
                        echo ""
                        echo "The removed revisions are not necessarily gone - if another reference"
                        echo "still refers to them they will stay in the repository."
                        rewind_only=1
                else
                        echo "This update added new revisions after undoing existing revisions.  That is"
                        echo "to say, the old revision is not a strict subset of the new revision.  This"
                        echo "situation occurs when you --force push a change and generate a repository"
                        echo "containing something like this:"
                        echo ""
                        echo " * -- * -- B -- O -- O -- O ($oldrev)"
                        echo "            \\"
                        echo "             N -- N -- N ($newrev)"
                        echo ""
                        echo "When this happens we assume that you've already had alert emails for all"
                        echo "of the O revisions, and so we here report only the revisions in the N"
                        echo "branch from the common base, B."
                fi
        fi

        echo ""
        if [ -z "$rewind_only" ]; then
                echo "Those revisions listed above that are new to this repository have"
                echo "not appeared on any other notification email; so we list those"
                echo "revisions in full, below."

                echo ""
                echo $LOGBEGIN
                show_new_revisions

                # XXX: Need a way of detecting whether git rev-list actually
                # outputted anything, so that we can issue a "no new
                # revisions added by this update" message

                echo $LOGEND
        else
                echo "No new revisions were added by this update."
        fi

        # The diffstat is shown from the old revision to the new revision.
        # This is to show the truth of what happened in this change.
        # There's no point showing the stat from the base to the new
        # revision because the base is effectively a random revision at this
        # point - the user will be interested in what this revision changed
        # - including the undoing of previous revisions in the case of
        # non-fast forward updates.
        echo ""
        echo "Summary of changes:"
        git diff-tree --stat --summary --find-copies-harder $oldrev..$newrev
}

#
# Called for the deletion of a branch
#
generate_delete_branch_email()
{
        echo "       was  $oldrev"
        echo ""
        echo $LOGEND
        git show -s --pretty=oneline $oldrev
        echo $LOGEND
}

# --------------- Annotated tags

#
# Called for the creation of an annotated tag
#
generate_create_atag_email()
{
        echo "        at  $newrev ($newrev_type)"

        generate_atag_email
}

#
# Called for the update of an annotated tag (this is probably a rare event
# and may not even be allowed)
#
generate_update_atag_email()
{
        echo "        to  $newrev ($newrev_type)"
        echo "      from  $oldrev (which is now obsolete)"

        generate_atag_email
}

#
# Called when an annotated tag is created or changed
#
generate_atag_email()
{
        # Use git for-each-ref to pull out the individual fields from the
        # tag
        eval $(git for-each-ref --shell --format='
        tagobject=%(*objectname)
        tagtype=%(*objecttype)
        tagger=%(taggername)
        tagged=%(taggerdate)' $refname
        )

        echo "   tagging  $tagobject ($tagtype)"
        case "$tagtype" in
        commit)

                # If the tagged object is a commit, then we assume this is a
                # release, and so we calculate which tag this tag is
                # replacing
                prevtag=$(git describe --abbrev=0 $newrev^ 2>/dev/null)

                if [ -n "$prevtag" ]; then
                        echo "  replaces  $prevtag"
                fi
                ;;
        *)
                echo "    length  $(git cat-file -s $tagobject) bytes"
                ;;
        esac
        echo " tagged by  $tagger"
        echo "        on  $tagged"

        echo ""
        echo $LOGBEGIN

        # Show the content of the tag message; this might contain a change
        # log or release notes so is worth displaying.
        git cat-file tag $newrev | sed -e '1,/^$/d'

        echo ""
        case "$tagtype" in
        commit)
                # Only commit tags make sense to have rev-list operations
                # performed on them
                if [ -n "$prevtag" ]; then
                        # Show changes since the previous release
                        git rev-list --pretty=short "$prevtag..$newrev" | git shortlog
                else
                        # No previous tag, show all the changes since time
                        # began
                        git rev-list --pretty=short $newrev | git shortlog
                fi
                ;;
        *)
                # XXX: Is there anything useful we can do for non-commit
                # objects?
                ;;
        esac

        echo $LOGEND
}

#
# Called for the deletion of an annotated tag
#
generate_delete_atag_email()
{
        echo "       was  $oldrev"
        echo ""
        echo $LOGEND
        git show -s --pretty=oneline $oldrev
        echo $LOGEND
}

# --------------- General references

#
# Called when any other type of reference is created (most likely a
# non-annotated tag)
#
generate_create_general_email()
{
        echo "        at  $newrev ($newrev_type)"

        generate_general_email
}

#
# Called when any other type of reference is updated (most likely a
# non-annotated tag)
#
generate_update_general_email()
{
        echo "        to  $newrev ($newrev_type)"
        echo "      from  $oldrev"

        generate_general_email
}

#
# Called for creation or update of any other type of reference
#
generate_general_email()
{
        # Unannotated tags are more about marking a point than releasing a
        # version; therefore we don't do the shortlog summary that we do for
        # annotated tags above - we simply show that the point has been
        # marked, and print the log message for the marked point for
        # reference purposes
        #
        # Note this section also catches any other reference type (although
        # there aren't any) and deals with them in the same way.

        echo ""
        if [ "$newrev_type" = "commit" ]; then
                echo $LOGBEGIN
                git show --no-color --root -s --pretty=medium $newrev
                echo $LOGEND
        else
                # What can we do here?  The tag marks an object that is not
                # a commit, so there is no log for us to display.  It's
                # probably not wise to output git cat-file as it could be a
                # binary blob.  We'll just say how big it is
                echo "$newrev is a $newrev_type, and is $(git cat-file -s $newrev) bytes long."
        fi
}

#
# Called for the deletion of any other type of reference
#
generate_delete_general_email()
{
        echo "       was  $oldrev"
        echo ""
        echo $LOGEND
        git show -s --pretty=oneline $oldrev
        echo $LOGEND
}


# --------------- Miscellaneous utilities

#
# Show new revisions as the user would like to see them in the email.
#
show_new_revisions()
{
        # This shows all log entries that are not already covered by
        # another ref - i.e. commits that are now accessible from this
        # ref that were previously not accessible
        # (see generate_update_branch_email for the explanation of this
        # command)

        # Revision range passed to rev-list differs for new vs. updated
        # branches.
        if [ "$change_type" = create ]
        then
                # Show all revisions exclusive to this (new) branch.
                revspec=$newrev
        else
                # Branch update; show revisions not part of $oldrev.
                revspec=$oldrev..$newrev
        fi

        git rev-parse --not --branches | grep -v $(git rev-parse $refname) |
        if [ -z "$custom_showrev" ]
        then
                git rev-list --pretty --stdin $revspec
        else
                git rev-list --stdin $revspec |
                while read onerev
                do
                        eval $(printf "$custom_showrev" $onerev)
                done
        fi
}


send_mail()
{
        if [ -n "$envelopesender" ]; then
                /usr/sbin/sendmail -t -f "$envelopesender"
        else
                /usr/sbin/sendmail -t
        fi
}

# ---------------------------- main()

# --- Constants
LOGBEGIN="- Log -----------------------------------------------------------------"
LOGEND="-----------------------------------------------------------------------"

# --- Config
# Set GIT_DIR either from the working directory, or from the environment
# variable.
GIT_DIR=$(git rev-parse --git-dir 2>/dev/null)
if [ -z "$GIT_DIR" ]; then
        echo >&2 "fatal: post-receive: GIT_DIR not set"
        exit 1
fi

projectdesc=$(sed -ne '1p' "$GIT_DIR/description")
# Check if the description is unchanged from it's default, and shorten it to
# a more manageable length if it is
if expr "$projectdesc" : "Unnamed repository.*$" >/dev/null
then
        projectdesc="UNNAMED PROJECT"
fi

recipients=$(git config hooks.mailinglist)
announcerecipients=$(git config hooks.announcelist)
envelopesender=$(git config hooks.envelopesender)
emailprefix=$(git config hooks.emailprefix || echo '[SCM] ')
custom_showrev=$(git config hooks.showrev)

# --- Main loop
# Allow dual mode: run from the command line just like the update hook, or
# if no arguments are given then run as a hook script
if [ -n "$1" -a -n "$2" -a -n "$3" ]; then
        # Output to the terminal in command line mode - if someone wanted to
        # resend an email; they could redirect the output to sendmail
        # themselves
        PAGER= generate_email $2 $3 $1
else
        while read oldrev newrev refname
        do
                generate_email $oldrev $newrev $refname | send_mail
        done
fi
# vim: set expandtab shiftwidth=4
